@figgin You are a star!! This worked (sort of). Basically i followed all you points until change password.

I went into Settings, click on wireless extender then extended network. From here your menu should show connect to  host network. you will see the 2.5 and 5 GHz and boxes that say password! Select this and copy, the find the extender network in wifi selection and paste the very long pw and presto instant connection :). 4 hours of back and forth via tech support and you've succeeded in minutes.

Thank you

@Tony 

I am having the same problem. EVENTUALLY set up with Tether, what a palaver that was! Linked the repeater to my router, same password. I can connect with my Macbook but when I try with my phone it says incorrect password. I have NEVER had a problem connecting to any other network, so why this one? I have rebooted my phone but it makes no difference. I have reset the repeater 4 times and the same problem occurs.

I have an old tp link repeater that did not need an App or all this rubbish, just plugged it in and it came up automatically on my computer and set it up in 2 minutes. Why does everyone need to complicate something that works?

@Carl 

My Router does not have a WPS button.

@Andy_C74   Hello...  I am having the same problem.  Did you resolve it?

@Amy129 Yes did you do what I said? Go into your router and find its IP number, then go on a browser and log into your extender and change password